The present invention relates, in general, to optical sensors utilizing vertical cavity surface emitting lasers (VCSELs), and in particular, to a method and system for efficient and versatile packaging of such optical sensors.
The Vertical Cavity Surface Emitting Laser (VCSEL) is rapidly becoming a workhorse technology for semiconductor optoelectronics. VCSELs can typically be used as light emission sources anywhere other laser sources (e.g., edge emitting lasers) are used and provide a number of advantages to system designers. Hence, VCSELs are emerging as the light source of choice for modern high volume applications such as optical encoders, reflective/transmissive sensors and optical read/write applications. Inherently low cost of manufacture, enhanced reliability, non-astigmatic and circularly symmetric optical output are just some of the advantages of VCSELs over traditional laser sources.
In many sensor applications, an optical sensor assembly scatters laser light off a surface and detects motion of the resulting optical speckle pattern through its movement across detectors disposed adjacent to the laser source or in some other convenient location exposed to the scattered light. The sensed motion can be in one or more axes, and the scattering surface can have many configurations, for example, a sphere, a cylinder, a plane, etc.
Typically, conventional optical sensor assemblies are produced using printed circuit board (PCB) or substrate-type materials with conventional surface mount processes and methods. The number and variety of assembly and alignment steps of such sensors must typically be done without the aid of mechanical locating features, and every feature must be affixed in a separate process. Such assembly processes are typically cost inefficient and generally produce optical sensors with undesirable tolerances and variances.
One example of such an assembly is illustrated in reference to FIGS. 1a and 1b, which depict front and rear side views of a VCSEL PCB assembly 100, respectively. In assembly 100, a VCSEL chip was mounted in a surface-mount component 102, which had a lens 104 as one of its piece parts. The lens 104 was attached in a solder process, and surface tension alone aligned it to component 102. Typically, this alignment process was not very efficient or accurate. Size constraints of the packaging and processes typically forced the VCSEL chip to be in close proximity to lens 104, resulting in angle of the exit beam varying as a function of chip position. The surface-mount component 102 was subsequently mounted to a conventional PCB 106. This operation typically led to additional misalignments, both through tilting of the component and through mis-positioning.
Typically, positioning of such an assembly to pins within an end-equipment housing was controlled by three drilled alignment holes 108. This resulted in further board-to-board variability. In fact, the pointing angle of the beam was typically so far from the intended axis that corrective rework was required, such as tilting the board by placing a shim over the appropriate hole. The remainder of the front side of assembly 100 included an individually mounted chip resistor 110 to set VCSEL power, two detector chips 112, and a ceramic spacer 114 added to the board to protect the detectors 112 and their bond wires from handling damage. On the rear surface of the board, high-temperature solder bumps 116 were typically formed in a separate operation. These bumps 116 were typically used as spatial stand-offs for positioning in the end equipment assembly. Additionally, the rear of the board may have had other structures, such as a metal disk and annulus (not shown), to provide end equipment functionality (e.g., to form conductors for a pressure sensitive button). Typically, these structures would be formed using thick, wire-bondable gold or another similar material which would often abrade and wear with use.
Thus, conventional methods and apparatus have required a variety of assembly and alignment steps, typically done without the aid of mechanical locating features, and typically affixing every feature in a separate process. Such assemblies and processes typically yield optical sensors with undesirable tolerances and variances in a cost inefficient manner. These approaches have further added to the production costs of sensor components and often change the electrical characteristics of the component, yielding different reliability and new characterization data for each component, reducing economies of scale in high volume sensor production.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
Versatile methods and apparatus for packaging optical sensors in a cost-effective and readily adaptable manner, while minimizing product variance, are needed, providing reduced optical variability and reduced misalignment sensitivity and an efficient production process while overcoming the aforementioned limitations of conventional methods.
In the present invention an optical sensor assembly is produced utilizing a single foundation piece formed with a light source housing, a lens alignment feature surrounding the light source housing, a mounting alignment feature, a sensor housing, and a barrier feature, a light source member mounted to the foundation piece within the light source housing, a single lens member enclosing the light source member and formed to engage with the lens alignment feature, and a detector member mounted to the foundation piece within the sensor housing.
In another embodiment of the present invention, a method of producing an optical sensor assembly is taught. The method comprises the steps of forming a foundation piece having a light source housing, a lens alignment feature surrounding the light source housing, a mounting alignment feature, a sensor housing, and a barrier feature, coupling a light source member to the foundation piece within the light source housing, forming a single lens member to enclose the light source member and engage with the lens alignment feature, coupling the lens member to the foundation piece, and coupling a detector member to the foundation piece within the sensor housing.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.